1. Field of the Invention
The present invention generally relates to a perpendicular electrode cell and a nonvolatile ferroelectric memory having the same, and more specifically, to a perpendicular electrode cell having an improved cell structure where a ceramic ferroelectric material used in a ferroelectric capacitor can be substituted with a ferroelectric polymer thin film having a perfect hysteresis loop curve with its small size which enables a low temperature process, and a nonvolatile ferroelectric memory using the same.
2. Background of the Prior Art
Generally, a ferroelectric random access memory (hereinafter, referred to as ‘FeRAM’) has a data processing speed as fast as a Dynamic Random Access Memory (hereinafter, referred to as ‘DRAM’) and conserves data even after the power is turned off.
The FeRAM having structures similar to the DRAM includes the capacitors made of a ferroelectric substance, so that it utilizes the characteristic of a high residual polarization of the ferroelectric substance in which data is not deleted even after an electric field is eliminated.
However, PZT and SBT which are ceramic dielectric materials used as conventional ferroelectric capacitor materials require a high temperature process of more than 600° C. and limit selection of electrodes of the capacitor. Also, the conventional ceramic ferroelectric materials have degraded uniformity in characteristics of each cell, which results in difficulty in improvement of yield.
In order to solve this problem, the conventional ceramic ferroelectric material is substituted with a ferroelectric polymer thin film. The ferroelectric polymer thin film includes P(VDF-TrFE), PVDF, Cyanopolymers, polyureas, polythioureas and odd-numbered nylons.
The ferroelectric polymer thin film can be processed at low temperature of less than 200° C., and has its size of 2Pr=5uC/cm2 but shows a perfect P-V hysteresis loop curve characteristic, so that it is advantageous in improvement of the uniformity of the cell. Also, the ferroelectric polymer thin film can reduce the process cost remarkably, improve the uniformity of the cell to advance productivity, and embody memory capacity of high density.
However, a conventional ferroelectric memory cell does not use the above-described ferroelectric polymer thin film materials because it has a structure that does not utilize process materials of low temperature (less than 200° C.).